Hitherto, realization of high transfer rate with respect to data recording/reproducing apparatus with improvement in processing speed of computer and increase in data quantity being as the background has been required. In order to allow the recording/reproducing apparatus to have high transfer rate, realization of high frequency of recording/reproduction signal is necessary. As one of the fundamental problem which obstructs realization of high frequency, operating speed of the reproduction signal processing circuit is mentioned. For example, in an apparatus employing Trellis code modulate system which is the advanced digital modulation system, since the maximum likelihood decode calculating circuit for binarizing (discriminating) reproduction signal requires vast operation quantity, this is the problem in improvement in operating speed. Although the maximum likelihood decoding system is not described in detail here, it will be expected in future that more complicated digital modulation systems are developed for the purpose of improvement in error rate. As a result, there is the possibility that vast calculation quantity may not be processed on the real time basis.
Here, in the real time processing, arithmetic operation is carried out for high rate reproduction signals, which have been converted from analog to digital under the AD (Analog to Digital) conversion, without changing rate. Namely, when reproduction signal channel rate is 100 MHz, a signal processing circuit also processes data or signals with the same 100 MHz rate. In all the apparatuses in practical use at present, data or signals are processed under the real time processing.
Here, a tape streamer 400 which performs real time processing will be explained with reference to FIG. 1.
The tape streamer 400 is a magnetic recording/reproducing apparatus of the helical scan type which has a rotation drum unit composed of a rotation drum and a fixed drum, and is adapted for recording data to a magnetic tape 401 wound on the rotation drum unit over 180° when viewed from the drum center and for reproducing thus recorded data. The rotation drum has recording heads W1, W2 and reproducing heads R1, R2 arranged thereon. The recording heads W1, W2 are arranged on opposite sides of the rotation drum, or are so arranged as to be apart from each other by 180° when viewed from the drum center, and also the reproducing heads R1, R2 are arranged on the rotation drum similarly.
In a recording system 410 of this tape streamer 400, recording data of data rate of 100 MHz is distributed and delivered, through a recording head changeover switch 411, to recording amplifiers 412A, 412B, at which recording data are amplified. The recording data thus amplified are delivered, through rotary transformers 413A, 413B, to a pair of recording heads W1 and W2 provided at the rotation drum.
The recording head changeover switch 411 is caused to undergo switching control by recording head switching signal WSWP in such a manner that recording data WR1 is given as a recording signal of the first channel to the first recording head W1 for 180° time period during which the first recording head W1 is slidably in contact with the magnetic tape 401, and recording data WR2 is given as a recording signal of the second channel to the second recording head W2 for 180° time period during which the second recording head W2 is slidably in contact with the magnetic tape 401.
In a reproducing system 420, reproduction RF signals of 2 channels respectively having about 0.1 mV obtained by scanning, by a pair of reproducing heads R1, R2, respective recording tracks of the magnetic tape 401 on which recording data is recorded by a pair of recording heads W1, W2 of the recording system 410 provided at the rotation drum are amplified by reproduction amplifiers 421A, 421B of 2 channels disposed in the vicinity of the heads for the purpose of avoiding noise mixing, and are delivered to the fixed drum side through rotary transformers 422A, 422B. The reproduction RF signal thus obtained is delivered to a reproduction processing system 430 through a reproduction head changeover switch 423.
The reproduction head changeover switch 423 is caused to undergo switching control by reproducing head switching signal RSWP in such a manner that reproduction RF signal of the first channel obtained for 180° time period during which the first reproducing head R1 is slidably in contact with the magnetic tape 401 is selected, and reproduction RF signal of the second channel obtained for 180° time period during which the second reproducing head R2 is slidably in contact with the magnetic tape 401 is selected.
The reproduction processing system 430 is composed of an equalizing circuit 431 which is cascade-connected to the reproduction head changeover switch 423, an Analog to Digital Converter (ADC) 432, a PLL circuit 435, and a reproduction signal discrimination circuit 436.
The equalizing circuit 431 adjusts gain and/or phase frequency response so that channel transfer characteristic of the reproduction RF signal delivered through the reproduction head changeover switch 423 results in a desired characteristic. An output of the equalizing circuit 431 is digitized at the ADC 432, and is delivered, as reproduction RF data, to the reproduction signal discrimination circuit 436 such as Viterbi decoder, etc. through the PLL circuit 435.
Here, since it is necessary to sample clock (ADC clock) of the ADC 432 by sampling frequency more than channel frequency of 100 MHz, it is required that ADC clock ≧100 MHz.
The PLL circuit 435 extracts channel clock (reproduction clock) of 100 MHz from reproduction RF signal which has been caused to undergo waveform equalization by the equalizing circuit 431. The reproduction clock is utilized as operating clock of all signal processing circuits of the succeeding stage.
The reproduction signal discrimination circuit 436 binarizes reproduction RF data to output it as reproduction data.
In the reproducing system 420 in this tape streamer 400, all circuits must operate at the channel frequency (100 MHz). When either one of circuits has operating speed less than 100 MHz, bit missing would take place. Such signal processing synchronous with the channel frequency is called real time processing. Since there is a tendency that the channel frequency rises in order to meet requirement of realization of high transfer rate, real time processing becomes more difficult.
Here, the term opposite to the real time processing is post processing. Namely, this system is a system of temporarily storing, into frame memory, reproduction signal of high rate converted Analog to Digital (AD conversion) to read it at rate lower than that in AD conversion to process the reproduction signal at low rate, i.e., to perform post processing to thereby lessen load of the operating speed of the reproduction signal processing circuit. The recording/reproducing apparatus which has been put into use by post processing does not yet exist, but is used at the experimental stage, and has been put into use in measurement instrument.
Then, outline of the post processing circuit will be explained with reference to FIG. 2.
A reproducing system 420A shown in FIG. 2 serves to perform post processing at the reproduction processing system 430 of the reproducing system 420 in the tape streamer 400, and comprises, at a reproduction processing system 430A, frame memories 434A, 434B, PLL circuits 435A, 435B and signal discrimination circuits 436A, 436B of 2 channels which are respectively cascade-connected to a switch 433 for distributing reproduction RF data digitized by the ADC 432 to 2 channels.
The switch 433 is driven by reproduction head switching signal RSWP to distribute and deliver reproduction RF data of the first channel in which reproduction RF signal obtained by the first reproducing head RI has been digitized by the ADC 432 and reproduction RF data of the second channel in which reproduction RF signal obtained by the second reproducing head R2 has been digitized by the ADC 432 to the frame memories 434A, 434B of 2 channels. The reproduction RF data of the first channel is stored into the first frame memory 434 A at 100 MHz rate, and reproduction RF data of the second channel is stored into the second frame memory 434B at 100 MHz rate. The store operations with respect to the respective frame memories 434A, 434B have duty ratio of 50%.
In FIG. 2, the right side partitioned by dotted lines is a post processing circuit 450. Since the post processing circuit 450 operates at duty 100%, low speed of half rate (50 MHz) can be attained. If this technology is developed to provide four frame memories, it is possible to perform signal processing at 25 MHz rate.
In general, in broadcast equipment for business and/or computer back-up unit (tape streamer), etc., design is made such that confirmation operation called Read After Write (RAW), which reproduce data immediately after recording the data to confirm whether or not the data is correctly recorded, can be executed.
It is to be noted that discrimination as to whether or not data is correctly recorded is conducted by judgment of magnitude of reproduction signal voltage in the analog VTR, and is conducted by judgment of error rate in tape streamer which performs digital recording. Most cases where data is not correctly recorded are the cases where medium is defective and/or dust is attached on the head surface.
Here, operation immediately after recording in RAW does not mean that tape is rewound from the time when recording is completed to reproduce data, but means data is reproduced just immiediately after the data is recorded by the recording head. For example, in the magnetic recording/reproducing apparatus of the helical scan system, there is employed a configuration such that RAW operation is conducted by the next drum rotation of the recording drum rotation. In the magnetic recording/reproducing apparatus of the linear system, there is employed a configuration such that reproducing heads are disposed at the backward position of the recording head to thereby perform RAW operation.
Meanwhile, in the case where RAW function is realized in the tape streamer 400 of the helical scan system, recording heads W1, W2,reproducing heads R1, R2, rotary transformers 413A, 413B for recording and rotary transformers 422A, 422B for reproduction which transmit signals thereto, etc., which are disposed at close distances, operate at the same time. From this fact, in order to suppress crosstalk interference where recording signal is mixed into very weak reproduction signal, it is necessary to employ, e.g., as shown in FIG. 3, strong shield structure which electromagnetically shields the recording system 410 and the reproducing system 420 therebetween. Namely, recording signals delivered to recording heads W1, W2 through rotary transformers 413A, 413B from recording amplifiers 412A, 412B are signals of large amplitude ranging to 10 V, whereas reproduction RF signals obtained at reproducing heads R1, R2 from the magnetic tape 401 are very small amplitude signal of the order of 0.1 mV, and its voltage ratio is fifth power of 10. Accordingly, shield as large as 100 dB must be implemented to recording signal. In order to obtain shield effect as large as 100 dB, space for inserting shield material is required. Employment of strong shield structure obstructs miniaturization of drum, leading to the cause to obstruct miniaturization of equipment.
As a technology for suppressing crosstalk interference from recording signal to reproduction signal by signal processing without employment of the shield structure in order to suppress crosstalk interference from recording signal to reproduction signal, e.g., technologies to subtract pseudo recording signal crosstalk generated by passing recording signal through the adaptive filter from reproduction signal to thereby remove crosstalk component of recording signal mixed into reproduction signal are disclosed in the Japanese Patent Application Laid Open No. 245307/1997 publication and/or the Japanese Patent Application Laid Open No. 177701/1998 publication.
If such crosstalk cancellation means is provided, error rate of RAW is improved. As a result, sense (detection) accuracy of head stain and/or tape defective which is the object of RAW is improved. Thus, this contributes to realization of high reliability of equipment.
Meanwhile, since crosstalk canceller is a circuit for canceling leakage of recording data, arithmetic processing had to be performed at recording data rate. Namely, real time processing had to be performed, and it was required to dispose crosstalk canceller at the preceding stage of frame memory. Accordingly, the crosstalk canceller is not permitted to undergo post processing, and the crosstalk canceller is required to perform 100 MHz rate operation. Thus, there is the possibility that the crosstalk canceller results in cause of obstacle (obstruction) to realization of high transfer rate.